Device for protecting polyphase circuits



Jan. 8, 1952 c. E. RANDALL 2,581,832

DEVICE FOR PROTECTING POLYPHASE CIRCUITS Filed Feb. 10, 1949 2Si-IEETS-SHEET 1 Inventor CYRIL. E.RAND'4 L.

B I /r y Arro%y Jan. 8, 1952 Q RANDALL 2,581,882

DEVICE FOR PROTECTING POLYPHASE CIRCUITS Filed Feb. 10, 1949 2SHEETS-SHEET 2 3 4/ 39 y k p g 37 H 42 24- 26 42 v3 I 3 f 2/ L1:

9 lln 23 [5 Inventor CYRIL E. RANDALL Art 091/ Patented Jan. 8, 1952DEVICE FOR PROTECTING POLYPHASE CIRCUITS Cyril E. Randall, Bedford,England, assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporationof Delaware Application February 10, 1949, Serial No. 75,613 In GreatBritain July 27, 1948 This invention relates to devices for protectingpolyphase circuits. The object of the invention is the provision ofimprovements in such devices and the invention consists broadly of adevice for protecting polyphase circuits against phase unbalance,comprising a plurality of elements together forming, in a mechanicalseries, a force-transmission means for retaining the device at a normalor non-tripped position, said elements being adapted to be individuallypositioned in a sense transversely to the direction of the forcetransmission, according to the current in the respective phases, and themechanical correlation of said elements being such that, upon thetransverse positioning of any neighboring pair relative to each other,departing, to more than a given extent, from the normal, the forcetransmission gives way so as to permit the device to move to the trippedposition.

In order that the invention may be the more clearly understood a devicein accordance therewith, together with a modification of said device.will now be described, reference being made to the accompanying drawingsin which:

Fig. 1 is a somewhat diagrammatic perspective view of said device.

Fig. 2 is a similar view of the left hand end of said device showing themodification.

Referring first to Fig. 1, the circuit to be protected is a three phasecircuit, and said circuit is interrupted upon disengagement of a movingcontact I from a fixed contact 2. Said contacts iand 2 may for examplebe connected in series with the winding of a three pole contactorcontrolling said three phase circuit.

-Said moving contact I is carried at the upper end of an upright leafspring 3 and said moving contact is controlled by means of an uprightpressure plate 4 which is mounted so as to be horizontally slidable.Said pressure plate 4 has a short horizontal projection 5 which engagessaid leaf spring, and when said pressure plate is slid to the right(according to the drawing) it presses said leaf spring to the right sothat the moving contact I engages with the fixed contact 2. When saidpressure plate is released said leaf spring presses said pressure plateto the left and simultaneously disengages said moving contact from saidfixed contact.

For guiding said pressure plate 4 to move horizontally as stated, theupper end of said pressure plate is slidable between horizontal guidemembers 6 and its lower end is slidable between horizontal guide membersI. To restrain said pressure plate against vertical movement, it hastransverse upper and lower pins 8 and 9 project ing from it, the upperpin 8 engaging the under surface of the guide members 6 and the lowerpin 9 engaging the upper surface of the guide members I.

7 Claims. (Cl. 200-113) Normally said pressure plate 4 is held at itsright hand position so that the contacts I and 2 are in engagement, but,upon the occurrence of either overload or voltage failure in one or twoof the phases, said pressure plate is released, enabling the contact ito leave the contact 2, and

causing the controlled circuit to be interrupted.

To this end three vertical sliding plates l0, ii and I2 are providedwhose upper ends slide between the upper guide members 6 and whose lowerends slide between the lower guide members I. These sliding plates areable to move not only horizontally, but also vertically, between theguide members. The sliding plates are controlled as to their verticalpositions by means of respective bi-metal elements l3, l4 and 15 whosetemperatures vary according to the current in the three phases. Theseelements 13, M and I5 are fixed at one end to fixed metal mountings l6,and their other ends are adapted to rise and fall according to theirtemperatures, that is according to the current value in the respectivephases. These movable ends engage in horizontal slots I! in therespective sliding plates, and thus, as the ends of the bimetal elementsrise and fall, said sliding plates also rise and fall. At the same timethe slots I! are sufficiently long to enable said sliding plates to maketheir horizontal components of movement independently of the bimetalelements.

The sliding plate ID has two projections l8 extending horizontally fromits right-hand edge and engaging the left hand edge of the pressureplate 4. Said sliding plate l0 also has two projections l9 extendinghorizontally from its left hand edge, and, when said sliding plate I0 isat the same horizontal level'as the sliding plate ll, these projectionsI9 abut, end to end, with two similar projections 20 extendinghorizontally from the right hand edge of the sliding plate I I. Saidsliding plate II has also two projections 2| extending horizontally fromits left hand edge, and. when said sliding plate II is at the samehorizontal level as the sliding p ate l2, these projections 2| abut, endto end, with two similar projections 22 extending horizontally from theri ht hand ed e of said sliding plate l2. Finallv said sliding plate l2has two projections 23 extending horizontally from its left hand edgeand abutting a a nst the right hand edge of a fixed vertical member 24.

Above the sliding plate I2 is provided a p n 7'5 which is ca able ofbeing adjusted vertically to a po it on which accords to the degree ofoverload at which it is desired to have the dev ce trip.

In op ration. assum ng the current in the controlled three phase circuitis switched oif. all three of the bimetal elements l3, II and i5 will beecually cold and the three plates l0, H and I2 will accordingly be atthe same level. Therefore the projections i9 and 28 will be inengagement, and so will the projections 2| and 22. The dimensions aresuch that, under these circumstances the pressure plate 6 is heldsufiiciently far to the right to cause the contact i to engage thecontact 2.

If now the current is switched on, and assuming that there is no voltageunbalance, the three bimetal elements will heat up equally and the threeplates II], II, l2 will rise together remaining at the same level. Theprojections i9 and 20 will remain in engagement, and so will theprojections 2| and 22. The projections ill will slide up the left-handedge of the pressure plate 5, and the projections 23 will slide up theright hand edge of the fixed member 24. The pressure plate 4 will remainunmoved and the contacts i and 2 will remain closed.

If now the current increases above the predetermined safe value, thesethree plates it, i i and I2 will continue to rise until the upper edgeof the plate l2 engages the pin 25. This prevents any further upwardmovement of said plate l2, but the plates II and ID will continue torise, until the projections 2i cease to register with the projections22, whereupon the pressure plate d together with the sliding plates isand ii are free to move to the left until the projections 2i engage theright hand edge of the sliding plate i 2, and/or the left hand edge ofthe sliding plate ii engages the prolection 22. This movement issumcient to enable the contact i to disengage the contact 2.

If instead of overload there has been a voltage failure in one or twophases, or some other voltage unbalance had taken place, a difference oflevel between certain of the plates ID, i l l2 would have eventuated sothat either the projections 2i 22 or the proiections i9, 22 would haveceased to register. Once again therefore the pressure plate 4 would havebeen free to move to the left, and the contact I would have disengaged.

In any event, for resetting the device after the bimetal elements haveagain become cold, a reset plate 26 is provided. This plate is mountedso as to be horizontally slidable in a plane parallel to the commonplane of the four plates i, i8, ii, i 2, and it carries transverse pegs27 which pass through apertures 28 in the sliding plate i9, and alsotransverse pegs 29 which pass through apertures 30 in the sliding platell. Said reset plate 26 is biased by means of a spring (not seen) to aleft hand limit as illustrated, and when it is pushed to the right i bymeans of a finger knob 3i mounted on it) the pegs 2i engage the righthand edges of the aperture 28 and press the plate ill to the right, andthe pegs 29 engage the right hand edges of the apertures 3t and pressthe plate H to the right. The pegs are so placed that the plate i ismoved sumciently in advance of the plate Ii to enable the projections isand 20 once more to comeinto line (if they had disengaged) so that theywill again abut against each other when the reset plate 28 is released.Equally the plate ii is moved in advance of the plate i2 so that theprojections 2i and 22 (if they had disengaged) will abut against eachother when the reset plate is released.

The reset plate 26 may also carry transverse pegs 31 which pass throughapertures 38 in the pressure plate 4. When the reset plate is pushed tothe right these pegs 3'! engage the right hand edges of the apertures 38before the pegs 27 engage the right hand edges of the apertures 29. Thusthe pressure plate 4 is kept clear of the pro- 4 jections l8 during theresetting operation. thereby making it easier for the bimetal elementsto return the sliding plates vertically to their correct levels.

In construction the guide members 6 are shown as forming the uppermember, and the guide members I the lower member, of a rectangular frameone of whose end members is constituted by the aforesaid member 24. Theother end member of said frame, which is designated by the reference 32,serves as the support on which the contact 2 and also the leaf spring 3are mounted.

The heating of the bimetal elements l3, l4 and it may be eilfectedeither by connecting them directly in the phases of the circuit to beprotected, or by means of heating coils (not shown) connected in saidphases.

The pin 25 is shown as mounted on an arm 33 which is pivoted at 34, sothat, by moving said arm about its pivot, the raising and lowering ofsaid pin 25 is effected. The extremity of said arm moves over, and readsagainst, a scale 35 which may be calibrated in terms of the currentvalue at which it is desired to have the de vice trip.

The whole structure is mounted on a suitable base 38.

Referring now to Fig. 2 this allows a modification in which, instead ofproviding the pin 2| for checking the upward movement of the plate I! onoverload so that the plates H and I0 continue to rise until they arefree to move to the left relative to said plate i2, an additionalvertical sliding plate 31 is provided between the plate" and thevertical member 24. This plate 31 has projections 38 extendinghorizontally from its right hand edge which normally abut end to endwith the projections 23 of the plate i 2. Said plate 311 is normallystationary during the operation of the device, and the projections 38are 01: considerable vertical depth as shown.

In operation, when the current is switched on, and assuming no voltageunbalance, the three plates l0, ii, i2 will rise together at the samelevel and the projections 23 will slide up the ends of the projections38, and the pressure plate 4 will remain unmoved and the contacts I and2 will remain closed. If, however, the current increases above thepredetermined sai'e value, the projections 23 will slide clear of theprojections 38, and the pressure plate 4, together with all thesesliding plates iii, ii and i2, will be free to move to the left andenable the contact I to disengage the contact 2.

Said plate 3'! has projections 39 from its left band edge which abutslidably against the right hand edge of the vertical member 24, and saidplate 31 is vertically adjustable, and it will be seen that its verticaladjustment determines the degree of overload at which the projections 23clear the projections 38. The vertical adjustment may be effected bypivotally connecting at $0 the *upper end of said plate M to theaforesaid arm 33. Thus the adjustment of said arm 33 determines thevertical adjustment of said plate 31, and said arm 33 indicates, asbefore, on the scale 35 the degree of overload to which the device isset.

The device functions exactly as before on phase unbalance. It will beseen that. for resetting the device, it will now be necessary to providethe reset plate 26 with additional transverse pegs M which pass throughadditional apertures 42 in the plate 02. Thus when the reset plate 2! ispressed to the right for resetting, the pegs 4| will engage the righthand edges of the apertures 42 and press the plate 12 to the right. Thepegs 4| are of course so placed that the plate ll moves suiliciently farin advance of the plate ii to permit the projections 2| and 22 tore-engage if they have been disengaged by phase unbalance, and at thesame time the plate 12 is moved sufllciently far to the right to enablethe projections 23 and 38 to re-engage if they have been disengaged byoverload.

I claim:

1. In a protective device for electric circuits wherein a relay is usedto control the circuit controllin switch in accordance with thecondition of a plurality of thermal responsive elements, each of whichelements is adapted to be heated in accordance with the current in aseparate conductor 01! the protect d circuit. tripping means for saidrelay com rising a plurality of sl de members. one for each thermalresponsive element, guide means for holding said members in coplanarrelationship and for permitting them to move only longitudinally andlaterally, a plurality of ,Dl'OjectiOlls extending laterallv fromadjacent edges of said movable members to prov de increased s acingbetween said members when the projections on adjacent members are inalignment with each other, means for connecting said mo able m mbe s tosaid thermal responsive elements to efiect longit dinal m v ment of saidmembers in accordance with the value of current in their respective conuctors, and means for biasing said re ay to tripped position, saidmovable members being normally positioned with their coo erating projctions in alignment to hold said relay in normal position against theforce of said biasing means. whereby upon an unbalance of curr nt in theconductors of the controlled circuit which causes the proiections to bemoved out of alignment at least one of sa d members wi l be movedlaterally to permit trip ing of said relay.

2. A releasing device for an electric switch comprisin in comb nation,means for normally biasing said switch to o en position. a plurality ofmovable members guided to move in a common plane and free for movementin said plane relative to each other. said members each havin laterallyextending projections arran ed for end-to-end en a ement w th similarprojections on adjacent members, said members being' positioned to ho dsaid s itch in closed position a ainst the force of said biasin meanswhen said pro ections are in enga ement, and a pluralitv of c rrent resonsive elements individually connected to said movable members to effectmovement thereof in parallel directions in accordance with the value ofcurrent controlling each element, whereby u on an unbalance in saidvalues of current the proiections on at least two adiacent movablemembers will move out oi en a ement to ermit transverse movement of atleast one of said members under the force oi said biasing means to o ensaid switch.

3. The combination with a switch having a movable element, of a fixedmember, a group of slide members interposed between said fixed memberand said movable switch element. said slide members bearing one a ainstanother and being of contour form such that the group is expansible orcontractable for exerting or relieving pressure on said switch elementby sliding any one of said slide members relative to an adjacent slidemember and current responsive means for effecting sliding of said slidemembers individually and selectively according to unbalanced currentconditions of said means.

4. The combination as in claim 3, wherein said movable switch elementhas stability during sliding of said slide members together, andincluding means for restricting the range of movement of one of saidslide members to permit sliding of another relative thereto underpredetermined current conditions.

5. A relay for polyphase alternating current circuits comprising thecombination with thermal elements for association with different phasesof the polyphase circuit of a switch having a movable element, a fixedmember, a. group of slide members interposed between said fixed memberand said movable switch element, said slide members bearing one againstanother and being of a contour form such that the group is expansible orcontractable for exerting or relieving pressure on said movable switchelement by sliding any one of said slide members relative to an adjacentslide member, said thermal elements each having connection with anassociated slide member for effecting sliding 01' said slide membersindividually and selectively according to unbalanced current conditionsin the different phases of the polyphase circuits.

6. A protective device for polyphase electric circuits comprising. incombination, a switch. means for biasing said switch to a givenposition, force transmission means for holding said switch in anotherposition against the force 0! said biasing means, said i'orcetransmission means comprising a plurality of slide members in end to endengagement and which upon a predetermined sliding movement of any onerelative to the member enga ed thereby eilects a change in the forcetransmission means to permit said switch to move to said given position,and current responsive means for sliding said slide membersindependently of one another for relative movement thereof when they aresubjected to unbalanced current, said slide members havin laterallyextending pro ections arranged for end to end engagement with similarprojections on adjacent members for eiteciing a reduction in theeffective length of said force transmission means upon movement of saidprojections out oi engagement with each other.

'7. A device according to claim 6, wherein a resetting member isprovided for engagin each 01 the slide members after the first and movinthem in the direction of force transmission, said slide members havingapertures formed therein,

engagement being effected bv transverse proiections on said resettingmember which pass throu h said apertures in said slide members forengagement with the walls 01' said apertures. whereby each member ismoved suiiiciently far in advance of the preceding one to enable them toreturn to normal relative positions.

CYRIL E. RANDALL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Besag May '1, 1940

